Aqueous hydraulic cement composition having improved retardation to set and use thereof in high temperature environments

ABSTRACT

In a method of cementing at relatively high ambient temperatures employing an aqueous hydraulic cement slurry, the improvement comprising admixing therewith an effective amount of both (1) a salt of lignosulfonic acid and (2) boric acid or a borate whereby a synergistic retarding effect on the setting rate of the slurry is attained without any accompanying adverse effects.

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S-lb-YZ AU 112 EX vuucu Dlaes Martin May 16, 1972 AQUEOUS HYDRAULIC CEMENT [56] References Clted COMPOSITION HAVING IMPROVED N TED STATES PATENTS gggggggg g gggggggggg W1... ENVIRONMENTS 2,292,616 8/1942 Dalley 106/3 15 Robert C. Martin, Tulsa, Okla.

The Dow Chemical Company, Midland, Mich.

Filed: June 1, 1970 Appl. No.: 42,569

Inventor:

Assignee:

2,211,368 8/1940 Dickens ..106/315 Primary Examiner-Tobias E. Levow Assistant Examiner-W. T. Scott Attorney-Griswold & Burdick and Charles W. Carlin ABSTRACT acid or a borate wheremcrglstic'fefirdfig effect on t e setting rate of the slurry 1s attained without any accompanying adverse effects.

5 Claims, No Drawings AQUEOUS HYDRAULIC CEMENT COMPOSITION HAVING IMPROVED RETARDATION TO SET AND USE THEREOF IN HIGH TEMPERATURE ENVIRONMENTS BACKGROUND OF THE INVENTION Aqueous cement slurries are frequently desired to be used for construction of buildings, surfacing (e.g. roads, parking lots etc.) and in underground cementing operations, e.g. in geologic formations penetrated by a wellbore (usually employed therein for purposes for securing a casing in place or for water or brine shut-off), and in tunnels, dams, or reservoir constructions, wherein the ambient temperature is often relatively high thereby accelerating the rate of setting cement of the slurry to one which is too fast to permit adequate time for the preparation of the slurry and its proper emplacement in the formation allowing an acceptable safety margin for a satisfactory job.

There have been introduced into the art of cementing additaments to cement slurries for the purpose of retarding the rate of set, of various types, and in some instances the results have been promising.

However, the problems of controlling the setting rate of cement slurries at high temperatures without impairment of the ultimate strength values of the cement has not been fully solved and are especially persistent where well cementing jobs (with increasing frequency as the years go by) are often performed at ever greater depths wherein often the bottom hole temperature is much higher than can be accommodated by the use of conventional cement slurries even containing the additives in accordance with the latest advancements heretofore known.

Conventional cement slurry compositions usually employed in cementing of wells comprise (I) an hydraulic cement, i.e. Portland, aluminous, pozzolanic, or expansive cements, or mixtures thereof and sometimes also containing gypsum or the like, (2) water, and optionally (3) as need dictates, additional functional control agents for such properties as rate of setting (usually a function of thickening rate), fluid-loss to a porous material (e.g. a loosely consolidated geologic formation) in contact therewith during the setting period, and/or frictionreducing agents effective during movement through tubes, pipes, casings, and the like. Such compositions are known as neat cement. For most uses other than in association with wells, sand and also often gravel are admixed with the slurry to make concrete.

Fully acceptable thickening control agents or retardants to the rate of setting of hydraulic cement slurries have long been sought, especially those which are effective at relatively high ambient temperatures as, for example, those often encountered in downhole operations.

SUMMARY OF THE INVENTION The invention is an improved aqueous hydraulic cement slurry and method of cementing wells employing it. The slurry contains as a required additament an improved retardant to the rate of setting thereof to a monolithic solid without adverse effect on ultimate compressive strength or other desirable qualities. The additament is a heretofore unknown combination which is much more effective at the usual troublesome higher temperatures, than would be expected from the behavior of each of the components of the combination when used separately in such slurry, said combination retardant being I) an alkali metal, alkaline earth metal or alkali metal-alkaline earth metal salt of lignosulfonic acid and (2) boric acid or a borate, e. g. borax. Such combination results in a truly synergistic effect.

Excellent results are obtained at between about 175 F. and about 400 F. The invention is commonly practiced at between about 230 F. and about 350 F. There is seldom a need for use of the retardant at lower temperatures unless an exceptionally long setting period is desired. At temperatures above about 400 F. the time existing between mixing and emplacement may thereby be caused to be unduly short. However, if an extremely short setting period is desired, the invention will fill that need. The amount of the additive retardant based on parts by dry weight of the hydraulic cement present is between about 0.5 and about 5.0 parts of component l) and between about 0.5 and about 5.0 parts of component (2) to make a total of both (1) and (2) of between about 1.0 and 10.0 parts based on the dry weight of cement present. Between about 1 and 4.0 parts of each component are commonly and preferably employed.

Other ingredients may be present in the slurry if desired for their known effect e.g. for fluidloss control of which cellulose and its derivative esters and/or ethers or polystyrene sulfonate or polyvinyltoluene sulfonate are illustrative, or friction-loss control agents as described in U. S. Pat. No. 3,254,7l9.

Silica flour, admixed with the aqueous cement slurry, has been found beneficial in preventing strength retrogression as the slurry sets at advanced temperatures. However, the invention may be practiced without silica flour being present.

The ratio of cement to water is that commonly employed, which may be between about 30 and about 65 parts (preferably between 35 and 50 parts)'of water per hundred 'parts dry weight of cement.

The improved cement composition of the invention is emplaced in a geologic formation by way of a pipe assembly or conveyor system when the formation is penetrated by a wellbore; conventional pumping equipment and lay-out for well cementing are employed. Truck-mounted mixers provided with high velocity pumps are often used.

COMPARATIVE TESTS AND EXAMPLES OF THE lNVENTION The following basic recipe was followed in the comparative tests which are not illustrative of the practice of the invention:

100 parts by dry weight of Class H cement (as described in API RP 10B), 30 to 60 parts of water, and the amounts of either component (1) or (2); but not both (l) and (2), as shown in the following tables, were admixed. The borate used was a technical grade Na,B O,.l0H,O Class H cement is a high temperature cement and was used herein because it best represents practical operating or field usage under the conditions herein represented. Other cements can be used in the practice of the invention but may not be the best choice because Class H is especially made for use at unusually high temperatures.

The examples of the invention contain both components l and (2), water, and a Portland or aluminous cement.

SERIES ONE In this series, tests wherein only one of the salt of lignosulfonic acid or borax was present, are identified by capital letters. Examples of the invention are identified by numbers. Although silica flour was used in this series to impart additional strength to the set cement, it is not essential to the practice of the invention.

Tests and examples of Series One contained 35 parts by weight, per 100 parts of cement, of silica flour having an average particle size of between about 100 and about 200 mesh.

The composition employed both in the comparative tests and examples of the invention contained 46 parts of water per 100 parts dry weight of Class H cement.

Tests were conducted in accordance with API RP 103 for Testing Oil Well Cements and Cement Additives, as set out in Section 10 Schedule 11, 20,000-foot casing-cementing Well- Simulation Test, at 340 F. circulation temperature. The results are shown on Table I.

TABLE I Thickening Time of Class H Cement containing 35 percent by Weight of 100 to 200 mesh silica flour and of the Indicated Amounts either 1) Sodium Calcium Lignosulfonate or (2) Borax or Both l and (2) Tested according to AP] Casing Cementing Schedule 1 1 Simulated 20,000 feet and 340 F. Circulating Temperature.

it can be seen by examination of Table ii that a ratio of 1 pan of sodium calcium lignosulfonate to 3 parts of borax, present in the total amounts set forth, and tested according to API thickening any one of Schedules 7 to 10 resulted in greatly increased time time tested by 5 of setting (i.e. a retarded setting rate). The greater the total Pan American amount of the two-component retardant, the longer the time ratio oi consistometer in Retardant Percent total retardant (based on 100 parts cement by dry weight) (1) and z hoummmutes of setting, tested at any given schedule.

i3? 210 of Both ii) andiii iii? 1228 1Q SERlES THREE Do 1:3 1;23 Do 1:1 1:28

The test of this series was conducted to show the efficacy of D 6:1 1=21 Th b 2.6 oi Both (1) and (2)-. m the uivention when no silica flour 15 present. e parts y f weight of ingredients per 100 parts of Class H cement were: E311 532 water 46 and the sodium calcium lignosulfonate: borax retara 5:1 15? dant in a ratio of 1:1 by weight in a total amount of both of 1.5. 3 r it): .III: The length of time for complete set of the slurry was 24 hours 3 8 gg gg lignosumnate-m a 3 which was substantially the same as when silica flour is 3' Do an (2) "I: i 3 135% present. 24 hours at 380 F. after mixing and promptly pouring DO 3 1 f 2 into molds, the compressive strength was 1,857 psi. This 38: 5 i 12:88 shows that silica flour, although otherwise shown to be referable in some cementing situations, is not necessary for the pracsai ei te t qn Although the tests hereinbefore employed silica flour to lessen degradation at high temperature upon aging, this test shows that silica flour is not essential to the practice of the invention.

A field example demonstrating the practice of the invention in an oil field is performed as follows:

A 7 inch liner is to be cemented in an 8 )6 inch open hole using two cement systems which have been designed for the job. Samples of the field blends of the two systems and a sam- If either component or Component (2) had exerted the ple of the field mixing water are first submitted for thickening expected effect on the rate of retardation, as shown when used time tests prior to performing the job The composition f the alone (i.e. if no unexpected synergistic effect occurred) then 1 cemmt System is that set out i h example f s i Three part of each used together should have retarded the setting abovm rate the cumulative sum of 52 and 36 mmutes or 1 hour and The well conditions and characteristics of the cementing 28 minutes. However, the table shows that the retardation composition (taken from an actual well to be treated) are as caused by one part of each used together retarded the setting follows rate not less than 1 hour and 15 minutes and when a greater total amount than 1 part of each was employed the rate of reit is shown by Table 1 that the use of either sodium calcium lignosulfonate or borax alone does not adequately lessen the 25 rate of setting. However, it does show that when both the sodium calcium lignosulfonate and borax were present in ratios of from 1:5 to 5:1, i.e. a ratio range of 1 part ofcomponent (l):1 part to 25 parts of component (2), the efi'ect on the rate of setting was to slow such rate perceptibly as is desired. The 30 chromium lignosulfonate test was run to show that other lignosulfonates alone were no better than the calcium species.

tardation was in excess of 6 hours (actually setting at between l n i n lurry properties system 1 system 2 12 and 15 hours).

Depth-19,600 slurry weight 16.5 15.2 SERIES Two feet pounds per gallon BEST-363 F. slu ield in 1.382 1.338 This series of tests was conducted to ascertain the thickena gg ing time of Class H cement, again containing 35 percent by "BHCT-BZIF. water required in 5.24 5.44 weight of finely divided silica flour as in Series One, tested ac- Ealbns/sack cording to various schedules in Section 10 of AH RP 108. The 0 amount of retardant consisted of either one or both of the lignosulfonic acid salt and/or borax. The results are shown in Table 11.

Bottom hole ltltic temperature. Bottom hole circulating temperature.

TABLE u Prior testing of lab blends of field materials indicate the fol- Thickening Time of Class H Cement containing 35 percent of lowing thickening times:

Silica Four, by Weight, Retarded by the Indicated Amounts of (1) Sodium Calcium Lignin and/or (2) Borax as Tested According to the API Casing Cement Schedules indicated. 66 Cement Systems Thickening Time in Hr1Min Thickening time, hours: minutes; API schedules followed, tengaerature and simulated. epth Cement System i Cement System 2 6:03 Schedule 6 5:22 Schedule 6 1 part retards: of (l) and 3 parts of (2) based on parts cement by weight Compressive strengths for these systems varied from about 3: weight ratio of the lignosulfonate salt to borax at 12,000 feet 0. and 260 F. up to 12,000 psi at 380 F. and a concentration of 8: 2.0 of a 1:3 ratio of the lignosulfonate salt to borax.

1. The cement slurries so prepared and tested will then be pumped down the annulus between the casing and formation wall to secure the well casing in place. Conventional mixing and pump equipment are to be used.

5,300 psi at a low retardant concentration of 0.1 part of a 1:3

The cement slurries so emplaced would set at or near 5 hour-6 hour time periods as shown by the tests and would have very satisfactory compressive strength values. The retarded setting rate would enable the operators to perform the job without undue haste even though the downhole temperature is unusually high.

The examples demonstrate the efficacy of the combined retardant effects of the lignosulfonic acid salt and the boric acid salt when both are used in an effective amount and in an effective ratio.

I claim:

1. In the method of emplacing an aqueous hydraulic cement slurry selected from the class consisting of Portland, aluminous, pozzolanic and mixtures thereof in an environment where the ambient temperature is relatively high and retardation of the rate of setting of thecement slurry is an objective, the improvement comprising admixing in said slurry, an amount of a retardant comprising in synergistic combination, a component (1) from the class consisting of at least one of a water-soluble or water-dispersible salt of lignosulfonic acid and a component (2) from the class consisting of at least one of boric acid or water-soluble or water-dispersible borate, which is effective to retard the rate of set of said slurry up to a temperature of about 400 F, emplacing said slurry at the locus where cementing is desired, and allowing the slurry to set to a monolithic solid.

2. The method according to claim 1 wherein component l is sodium calcium lignosulfonate.

3. The method according to claim 1 wherein component (2) is borax or a borax hydrate.

4. The method according to claim 1 wherein said cement slurry is emplaced in a geologic formation penetrated by a borehole and the cement slurry is injected down the borehole at sufficient pressure and controlled conditions to locate it at the desired level and to force it into the formation to the extent desired.

5. The method according to claim 1 wherein there are present in said slurry up to 50 parts, based upon the dry weight of cement present, pulverulent silica of a mesh size of between about to about 200.

i i l i i 

2. The method according to claim 1 wherein component (1) is sodium calcium lignosulfonate.
 3. The method according to claim 1 wherein component (2) is borax or a borax hydrate.
 4. The method according to claim 1 wherein said cement slurry is emplaced in a geologic formation penetrated by a borehole and the cement slurry is injected down the borehole at sufficient pressure and controlled conditions to locate it at the desired level and to force it into the formation to the extent desired.
 5. The method according to claim 1 wherein there are present in said slurry up to 50 parts, based upon the dry weight of cement present, pulverulent silica of a mesh size of between about 100 to about
 200. 